1. Field of Invention
The technical scope of the present invention is that of laying systems for a weapon ensuring its stabilisation.
2. Description of Related Art
When a weapon is mounted on a mobile support, that is on a moving vehicle, laying operations become difficult to ensure, since the weapon is subjected to a certain number of disturbances. Firing from such a weapon requires it to be oriented in the direction of the target and this despite any movements, be they linear or angular, of the vehicle. One particularity of a vehicle able to move at high speeds (more than 50 km/h) cross country lies in the stresses it causes to the weapon and to its laying system and which generally correspond to a high level and cover a wide spectrum.                During displacements of the vehicle, these disturbances may notably come from:        the angular velocity of the support of which the weapon is mounted and which reach the weapon via the motorization system,        the linear acceleration applied to the turret's axis of rotation via the offsetting the turret's centre of gravity with respect to this axis,        the angular acceleration applied directly to the turret by the friction that appears on the circular bearing, friction caused in particular by the sealing means to be set in place between the turret and the chassis,        the angular acceleration of the support around an axis perpendicular to the two traverse axes of rotation of the turret and the weapon's elevation axis of rotation via a coefficient depending on the elevation of the weapon.        
Three types of limitations deteriorating the traverse orientation efficiency of the weapon may thus be found. Firstly, the weapon's positioning accuracy is adversely affected by the friction because of the presence of a large diameter bearing and its associated seals. Moreover, on the one hand the motorization torque available for the turret limits the possibilities of compensating the roll effect on the orientation of the weapon, whereas on the other, the stabilisation error associated with this type of disturbance is particularly great.
Several methods and devices are known to attenuate the roll effects on the firing performances of a weapon.
A first method consists in measuring the perturbing angular velocity, for example using geometric type means, and using this measurement to control the rotational speed of the motorization system placed between the support and the weapon. It is thus an anticipatory control placed in parallel with a servo control of the weapon's position on an inertial reference whose efficiency is low so as to attenuate the amplitude of the angular disturbances at mean frequencies. Reference may be made, for example, to patent FR-80.21077.
Another method consists in providing motorization means allowing the torque applied to the load to be controlled. This principle is used to improve the efficiency of the reduction of the effects of the angular velocity disturbances. This method is adapted to low offset values. Reference may be made, for example, to patent U.S. Pat. No. 4,387,624.
Yet another method consists in measuring the gyrometric roll velocity and in controlling an angular velocity of the turret that is proportional to this velocity, via a coefficient depending on the elevation of the weapon. Although this method allows the quality of stabilisation provided by the servo-control of the weapon on the inertial reference to be improved, it is firstly limited in efficiency and secondly rapidly reaches the limits of the motorization's torque capacities.
When the elevation of the weapon and the angular roll velocities increase, in spite of the quality of the controls given to the traverse motorization, the quality of the stabilisation deteriorates and the limitations imposed by the size of the motorization in position are rapidly attained.
When driving cross country at high speed, two limitations thus deteriorate the possibility of maintaining good traverse orientation of a weapon laid on a target. Firstly, the weapon's positioning accuracy is affected by the friction because of the presence of a large diameter bearing and its associated seals. Furthermore, on the one hand the torque available for the motorization of the turret limits the possibility of compensating the roll effect on the weapon's acceleration whereas, on the other the error associated with this type of disturbance is great.